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Photon‐Stimulated Desorption of MgS as a Potential Source of Sulfur in Mercury's Exosphere
Author(s) -
Schaible Micah J.,
Sarantos Menelaos,
Anzures Brendan A.,
Parman Stephen W.,
Orlando Thomas M.
Publication year - 2020
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1029/2020je006479
Subject(s) - exosphere , ionization , mercury (programming language) , sulfur , analytical chemistry (journal) , chemistry , atomic physics , mass spectrometry , ion , physics , environmental chemistry , organic chemistry , chromatography , computer science , programming language
Mercury has a relatively high sulfur content on its surface, and a signal consistent with ionized atomic sulfur (S + ) was observed by the fast ion plasma spectrometer (FIPS) instrument on the MESSENGER spacecraft. To help confirm this assignment and to better constrain the sources of exospheric sulfur at Mercury, 193 nm photon‐stimulated desorption (PSD) of neutral sulfur atoms (S 0 ) from MgS substrates was studied using resonance‐enhanced multiphoton ionization (REMPI) spectroscopy and time‐of‐flight (TOF) mass spectrometry. Though the PSD process is inherently nonthermal, the measured velocities of ejected S 0 were fit using flux‐weighted Maxwellian distributions with translation energies expressed as translational “temperatures” T t rans = /μk B . A bimodal distribution consisting of both thermal (T t rans = 300 K) and suprathermal (T t rans > 1,000 K) components in roughly a 2:1 ratio was found to best fit the data. The PSD cross‐section was measured to be approximately 4 × 10 −22 cm 2 and, together with the velocity distributions, was used to calculate the PSD source rate of S 0 into the exosphere of Mercury. Exosphere simulations using the calculated rates demonstrate that PSD is likely the primary source of S 0 in Mercury's exosphere at low (<1,000 km) altitudes.